In water desalinisation equipment using the principle of evaporation to remove salt and other minerals, it is customary to have an evaporator in which conditions are so adjusted that steam or vapour is formed which is then taken to a heat exchanger whereby the steam is condensed to provide the distilled water.
In such systems it is customary to feed brine into the evaporator from a constant level supply and to then so adjust conditions between the evaporator and the heat exchanger that the necessary transfer of the vapour will take place, such a method including for instance the use of a pump which moves the vapour to the heat exchanger.
Among these systems embodying this general principle are those in which refrigeration equipment is used to evaporate water at ambient or raised temperature, the evaporator of the refrigeration system being connected to the condenser through pump means, the condenser ensuring that the steam or vapour is brought back to its liquid phase to form the distillate.
It has also been proposed by us in such a system to use what we term a "blow-down" pump which draws off excess water from the evaporator when the salinity of that water reaches a certain value, this then ensuring that the products left behind in the evaporation process are washed out of the system so that the process can be a continuous one.
One of the problems encountered in apparatus of this type is to be able to maintain correct movement of the vapour or steam, and also to maintain the necessary pressure differentials in the system because obviously in the evaporator a lowered pressure must exist to ensure ready boiling of the liquid while in the condenser it may be preferable to have a higher pressure to ensure ready condensation of the vapour.
As the pumps must be of a nature such that they can draw the necessary vacuum in the condenser, problems exist in achieving good seals in such pumps, and according to one of our earlier Patent Applications a system of water seals was used so that relatively inexpensive gear pumps could be used for the drawing of the vacuum.
The object of the present invention is to provide an improved pumping system for use in evaporative distillation plants of the general type outlined whereby the necessary seals can be readily obtained and in which in the ultimate form it is unnecessary to use expensive condensers and evaporators.